In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
For the boring of deep holes in rock or earth, drill strings are used, which comprise a plurality of rods and coupling sleeves, which are assembled as the depth of the hole increases. A terrestrial machine having a shank adapter has the purpose of transferring combined impact and rotary motions to the upper end of the drill string, the lower end of which carries a drill bit, which performs the active operation to crush the rock and form the hole. By flushing fluid through the drill string to the drill bit, the detached drill cuttings can be conveyed to the hole entry by passing between the outside of the drill string and the inside of the hole.
In rock drilling equipment of this type, a number of requirements and needs are made, one of which is that the recessed hole should be as straight as possible, for instance in order to in the best way impinge on a predetermined target deep down in the rock. For this purpose, a number of control devices have previously been proposed, which make use of tubular controlling elements adjacent to those coupling sleeves, which couple together the different rods, or alternatively along the proper rods. Disadvantages of this type of control devices are that the drilling equipment in its entirety becomes complicated, expensive and ungainly to handle. A previously known rock drill bit, which to a certain extent has improved the straightness of drilled holes is shown in U.S. Pat. No. 7,281,594. A number of steps have there been provided on the skirt of the drill bit, which steps guide the bit in succession.
Another requirement is that the components included in a rock drilling equipment, and in particular the expensive drill bit, should have an optimum service life. In order to provide for this requirement, it is among other things important that the internal thread of the rear skirt of the drill bit is turned by smooth and precision-shaped thread ridges and thread grooves, because otherwise tendencies to crack and other phenomena may arise, which result in early corrosion fatigue